The detection of herpesvirus DNA in Kaposi's sarcoma (KS) lesions from persons with the acquired immunodeficiency syndrome (AIDS) opens new directions in the study of the epidemiology, prevention, and therapy of this malignancy (1). Although past epidemiological evidence suggesting that KS may be caused by an infectious agent is supported by this discovery (2-5), the role of this new herpesvirus in the pathogenesis of KS has yet to be determined. This new virus has been named Kaposi's sarcoma-associated herpesvirus (KSHV) or human herpesvirus 8 (HHV-8) (1,6). Characterizing the types of cells infected by KSHV may facilitate development of tissue culture models to propagate and further study this virus in addition to expanding our understanding of the epidemiology and biology of both KSHV and KS. The goals of this study are to explore the types of cells infected by KSHV in persons with AIDS and to identify genes expressed in latently infected cells. One hypothesis to be tested is that B lymphocytes are the primary reservoir for latent KSHV. The specific aims are: (a) to define and characterize the types of cells infected with KSHV; (b) to determine if KSHV infection of different cell types is latent or lytic; and (c) to clone and sequence viral or cellular genes selectively expressed during latent infection.